1. Field of the Invention
The present invention relates to a data acquisition system, and more particularly, to a system and method for acquiring data of a multi-channel signal.
2. Discussion of Related Art
A data acquisition system is a part of a measurement system acquiring and storing data. Engineers read a dial of a transducer to define a value according to the dial and record the information in a record book, which is the same as a task processed by a data acquisition system. For a task of acquiring, quantizing and storing data, a data acquisition system based on a datalogger collecting and storing a signal and a personal computer (PC) is used.
A voltage signal measured by a precise sensor in a magnetically shielded room (MSR) or radio-frequency shielded room (RFSR) is transmitted to a data acquisition (DAQ) board outside the shield room. The DAQ board is hardware converting a voltage signal output through a sensor or signal conditioning module into a digital signal that can be recognized by a computer. In general, a DAQ board installed in a computer acquires an output voltage signal and transfers it to the inside of the computer. The voltage signal transferred to the computer is stored in a storage, or analyzed and displayed on a monitor.
FIG. 1 illustrates a system for acquiring data of a multi-channel signal using a DAQ board.
Referring to FIG. 1, a system 10 for acquiring data of a multi-channel signal measures output signals of 256 channels to acquire data, and includes 256 wires 21, a ground wire 25, a plurality of DAQ boards 31 to 34, and a computer 35.
A voltage signal that is measured by a sensor in a shield room 40 is output from the shield room 40 through the 256 wires 21 and the ground wire 25, and input to the plurality of DAQ boards 31 to 34. When one DAQ board can have 64 channels, four DAQ boards are installed to receive a voltage signal output from the 256 channels.
The plurality of DAQ boards 31 to 34 convert an input voltage signal into a digital signal and send the digital signal to the computer 35. When there are a large number of DAQ boards, the DAQ boards are installed in a versa module Eurocard (VME) extensions for instrumentation (VXI) device rather than directly in the computer 35, and an output of the VXI device is sent to the computer 35.
FIG. 2 illustrates a system for acquiring data of a multi-channel signal using a channel module.
Referring to FIG. 2, a system 50 for acquiring data of a multi-channel signal measures an output signal of 16 channels to acquire data, and includes 16 wires 61, a ground wire 65, an analog switch 71, an analog-to-digital converter (ADC) 72, a clock/counter 73, a digital signal processor (DSP) 74, and a computer 80.
Voltage signals measured by a sensor in a shield room 90 are output from the shield room 90 through the 16 wires 61 and the ground wire 65, and input to the analog switch 71. The analog switch 71 selects an input signal and sends the selected signal to the ADC 72.
The ADC 72 converts the selected input voltage signal into a digital signal and sends the digital signal to the DSP 74. The clock/counter 73 sends an input channel selection signal for selecting an input channel to the analog switch 71, or sends a signal to the ADC 72 and the DSP 74 to connect them and synchronize the ADC 72 with the input channel. The DSP 74 processes the input digital signal and sends the processed digital signal to the computer 80.
To acquire data from 32 channels, a 32:1 analog switch and one ADC are used, or two 16:1 analog switches and two ADCs are connected in parallel. To acquire data from 256 channels, sixteen 16-channel modules or eight 32-channel modules are used.
In a system for acquiring data of a multi-channel signal using a DAQ board, the number of wires coming from a shield room increases in proportion to the number of channels, thereby bringing noise outside the shield room into the shield room. Direct connection between a ground wire of the shield room and a ground wire of the DAQ board also brings additional noise into the shield room. Further, loop-circuit noise is generated between the DAQ board and another DAQ board added to increase signal acquisition channels, and the additional DAQ board results in an increase in cost and a decrease in channel-specific sampling time.
To have 256 channels in a system for acquiring data of a multi-channel signal using a channel module, many modules and a VXI device installed with a module board are required. These make the system complicated and increase cost.